A Windows Domain Account is a user authentication profile created on an Windows Domain Controller.

A Windows Domain Account for a user usually contains a username and password
as the authentication mechanism.

You can use your Windows Domain Account to login to any computer
running Windows 7 or other Windows system and
connected to the domain controlled by the domain controller.

The main difference between a local account and a domain account
is that the local account can only let you login to one single computer.
The domain account can let you login to all computers in the domain.

Here is a diagram showing how a user can login to multiple computers
in a domain managed by a domain controller: